Here you have in a C code written Serial Initialize routine. The code also include assembler.



/*------------------------------------------------------------------------------
SIO.C: Serial Communication Routines.

Copyright 1995-1996 KEIL Software, Inc.
------------------------------------------------------------------------------*/

//#include <reg51.h>
//#include <string.h>
//#include "sio.h"

/*------------------------------------------------------------------------------
------------------------------------------------------------------------------*/
#define TBUF_SIZE 256 /* DO NOT CHANGE */
#define RBUF_SIZE 256 /* DO NOT CHANGE */

#define OSC 11059200 /* Oscillator Frequency */

static xdata unsigned char tbuf [TBUF_SIZE];
static xdata unsigned char rbuf [RBUF_SIZE];
static xdata unsigned char t_in = 0;
static xdata unsigned char t_out = 0;
static xdata unsigned char t_disabled = 0;

static xdata unsigned char r_in = 0;
static xdata unsigned char r_out = 0;
extern void init_message_level(void);

/*------------------------------------------------------------------------------
------------------------------------------------------------------------------*/
static void com_isr (void) interrupt 4 using 2
{
/*------------------------------------------------
Received data interrupt.
------------------------------------------------*/
if (RI != 0)
{
RI = 0;

if ((r_in + 1) != r_out)
rbuf [r_in++] = SBUF;
}

/*------------------------------------------------
Transmitted data interrupt.
------------------------------------------------*/
if (TI != 0)
{
TI = 0;

if (t_in != t_out)
SBUF = tbuf [t_out++];
else
t_disabled = 1;
}

}

/*------------------------------------------------------------------------------
------------------------------------------------------------------------------*/
void com_initialize (void)
{
/*------------------------------------------------
Setup TIMER1 to generate the proper baud rate.
------------------------------------------------*/
com_baudrate (19200);
/*------------------------------------------------
Clear com buffer indexes.
------------------------------------------------*/
EA = 0; /* Disable Interrupts */

t_in = 0;
t_out = 0;
t_disabled = 1;

r_in = 0;
r_out = 0;

/*------------------------------------------------
Setup serial port registers.
------------------------------------------------*/
SM0 = 0; SM1 = 1; /* serial port MODE 1 */
SM2 = 0;
REN = 1; /* enable serial receiver */

TI = 0; /* clear transmit interrupt */
RI = 0; /* clear receiver interrupt */

ES = 1; /* enable serial interrupts */
PS = 0; /* set serial interrupts to low priority */

EA = 1; /* Enable Interrupts */

}

/*------------------------------------------------------------------------------
------------------------------------------------------------------------------*/
void com_baudrate (
unsigned baudrate)
{
EA = 0; /* Disable Interrupts */

/*------------------------------------------------
Clear transmit interrupt and buffer.
------------------------------------------------*/
TI = 0; /* clear transmit interrupt */
t_in = 0; /* empty transmit buffer */
t_out = 0;
t_disabled = 1; /* disable transmitter */

/*------------------------------------------------
Set timer 1 up as a baud rate generator.
------------------------------------------------*/
TR1 = 0; /* stop timer 1 */
ET1 = 0; /* disable timer 1 interrupt */

PCON |= 0x80; /* 0x80=SMOD: set serial baudrate doubler */

TMOD &= ~0xF0; /* clear timer 1 mode bits */
TMOD |= 0x20; /* put timer 1 into MODE 2 */

TH1 = (unsigned char) (256 - (OSC / (16L * 12L * baudrate)));

TR1 = 1; /* start timer 1 */

EA = 1; /* Enable Interrupts */
}



/*------------------------------------------------------------------------------
------------------------------------------------------------------------------*/
char com_putchar (
unsigned char c)
{
/*------------------------------------------------
If the buffer is full, return an error value.
------------------------------------------------*/
if ((TBUF_SIZE - com_tbuflen ()) <= 2)
return (-1);

/*------------------------------------------------
Add the data to the transmit buffer. If the
transmit interrupt is disabled, then enable it.
------------------------------------------------*/
EA = 0; /* Disable Interrupts */

tbuf [t_in++] = c;

if (t_disabled) /* if transmitter is disabled */
{
t_disabled = 0;
TI = 1; /* enable it */
}

EA = 1; /* Enable Interrupts */

return (0);
}

/*------------------------------------------------------------------------------
------------------------------------------------------------------------------*/
char com_getchar (void)
{
char c;

if (com_rbuflen () == 0)
return (-1);

EA = 0; /* Disable Interrupts */
c = rbuf [r_out++];
EA = 1; /* Enable Interrupts */

return (c);
}

/*------------------------------------------------------------------------------
------------------------------------------------------------------------------*/
unsigned char com_rbuflen (void)
{
return (r_in - r_out);
}

/*------------------------------------------------------------------------------
------------------------------------------------------------------------------*/
unsigned char com_tbuflen (void)
{
return (t_in - t_out);
}

/*------------------------------------------------------------------------------
------------------------------------------------------------------------------*/